An outage has knocked TalkTalk’s website offline, along with internal systems.
The company tweeted that it was working on addressing the problems:
We are aware of issues affecting our website and help pages at the moment. We're working to restore this asap. http://t.co/wWauH89kHP
— TalkTalk (@TalkTalkCare) August 21, 2015 …

VoIP

"On Twitter it asked customers to call after 1pm, and their internal VoIP and data systems are affected."

Well, this is the bunch that told me VoIP won't work over ADSL, it needs a leased line or at least FTTC, so not too surprising they've managed to make a pig's ear of their own too!n (That, and "40 Gb per month is too much usage for an "unlimited" business ADSL line", got us to move to a proper ISP.)

Rather, I used to be a customer of a company they bought, which was sort of OK, but whose usage meters never worked.

That company never seemed this incompetent, but I never heard anything from either about IPv6. I'm not sorry I moved, Some of the boys in the internet business are so wide that it's a long walk round them.